It is well known that users of power supplies for microprocessors are demanding higher current and lower output voltage. As current goes to 130 A, and even higher, the total conduction loss of conventional converters is significantly increased thereby causing severe thermal issues. To lower the on resistance of a conventional synchronous rectifier, more semiconductor devices are used. Furthermore, distributed magnetics are also used to reduce transformer winding losses. These solutions, however, typically result in higher cost and footprint increases while the power density decreases. Additionally, more device means more driving loss. These issues pose substantial challenges for future high current low voltage DC/DC converters used in microprocessors.
Rectifier diodes in DC/DC converters have been substituted with synchronous rectifiers, which have lower voltage drops. Synchronous rectifiers in self-driven implementations are typically driven with the secondary voltage of the transformer. In an external-driven implementation, the synchronous rectifiers are driven by gate-drive signals derived from the main switches of the primary side. A partially external-driven method is possible. See Li Xiao, Ramesh Oruganti, “Soft Switched PWM DC/DC Converter with Synchronous Rectifiers”, in Telecommunications Energy Conference 1996. INTELEC'96, 18th International, 1996. pp. 476-484.
Self-driven synchronous rectifier circuits are known. For example, U.S. Pat. No. 6,370,044 issued to Zhang et al. discloses a self-driven synchronous rectifier circuit. The self-driven synchronous rectifier circuit of Zhang et al. utilizes a primary and secondary winding for converting an input voltage into an output voltage, a first and second synchronous rectifier switch connected to the secondary winding to rectify the output voltage, and an auxiliary switch. The gate terminal of the auxiliary switch is connected to the gate terminal of the first synchronous rectifier switch and the positive end of the secondary winding, the source terminal thereof is connected to the drain terminal of the first synchronous rectifier switch and the negative end of the secondary winding, and the drain terminal thereof is connected to the gate terminal of the second synchronous rectifier switch.
Zero voltage switching is known and refers to a circuit or device for opening and closing a circuit, or for connecting a line to one of several different lines, which operates in the complete absence of voltage or the lowest voltage in a circuit to which all other voltages are referred. It is known in the art to incorporate zero-voltage switching circuit configurations into converter applications. These ZVS configurations have been incorporated into either the primary or secondary side of converters. See R. Watson and F. C. Lee, “Analysis, design, and experimental results of a 1-kW ZVS-FB-PWM converter employing magamp secondary-side control,” IEEE Trans. Industrial Electronics., vol. 45, pp. 806-814, October 1998.
Furthermore, it is known in the art to provide transformer connections of coils or load devices with more than one-or two-phases. Three-phase transformer connections consist of three transformers that are either disposed separately on adjacent cores or combined on a single core. The primaries and secondaries of any three-phase transformer can be independently connected in either a wye (Y) or a delta (Δ) connection. A delta connection is used to connect an electrical apparatus to a three-phase circuit, the three corners of the delta are represented as being connected to the three wires of the supply circuit. The delta connection is a triangular connection and resembles a Greek letter delta.
A wye connection is also used for connecting an electrical apparatus to a three-phase circuit. The wye connection is a method of connecting three windings so that one terminal of each winding is connected to a neutral point. The wye connection is shaped like the letter Y. In three-phase transformer applications, the primary and the secondary can have either a wye or a delta connection. Four possible connections are available for the primary-secondary configuration. These are wye-wye, wye-delta, delta-wye and delta-delta. A three-phase transformer bank may be composed of independent transformers or wound on a single three-legged core. See Stephen J. Chapman, “Electric Mmachine and power system fundamentals”, McGraw-Hill Companies, Section 3.10, 2002.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed.